In coherent detection high-speed optical transmission system, due to the phase deviation between the corrected emission laser and the local oscillator laser at the receiving end, in order to eliminate the effects of the phase deviation on the signal judgment, the phase estimation algorithm is often used to compensate the phase deviation.
The VITERBI-VITERBI algorithm is a classical phase estimation algorithm. Its basic principle is to perform a biquadrate process to the phase of the received signal, then perform weighted average, and extract a phase compensation value. Because of the biquadrate operation, it is resulted that there is a phase ambiguity of positive and negative π/2 in the recovered phase. The phase ambiguity is solved mainly by estimating a phase offset through a mode of adding a training sequence. That is, the transmitting end introduces a standard training sequence among various data sequences when a data signal is sent, and the receiving end performs phase correction on a corresponding data sequence through a phase difference between the received training sequence and the standard training sequence after receiving the data signal.
In the traditional phase ambiguity training scheme, a section of training sequence is responsible for correcting the phase to a section of data sequence. FIG. 1 is a schematic diagram of phase ambiguity occurred in a middle part of an existing data sequence. As shown in FIG. 1, assuming that phase ambiguity is generated at the middle part of the data sequence (i.e., shaded area), in the existing phase ambiguity training method, the receiving end is unable to identify the phase ambiguity in the middle of the data sequence through the training sequence, therefore, in order to avoid the occurrence of the above situation, a section of data sequence should not be set to be too long, that is, a large number of training sequences are required to be introduced into the whole data signal to ensure the accuracy of the phase correction, thus, it will inevitably lead to excessive bandwidth cost.